1. Field
Embodiments of the invention relate generally to a nonvolatile memory device and a method for manufacturing the same.
2. Background Art
A resistance change memory has been drawing attention as a next-generation nonvolatile memory because it is less prone to characteristics degradation despite downscaling, and easily increased in capacity (see, e.g., JP-A 2007-184419 (Kokai)).
The resistance change memory is based on the characteristics of a resistance change film whose resistance changes when a voltage is applied to and a current is passed in the resistance change film. Such a resistance change film is made of various oxides, such as oxides of transition metals.
Conventional resistance change films require an initialization process (forming) for decreasing the resistance thereof, and hence are inefficient. Furthermore, forming requires a high forming voltage, which may destroy the resistance change film. Moreover, the switching operation (reset operation) for switching from the low-resistance state to the high-resistance state requires a large current, which makes it difficult to reduce power consumption.
In this context, a method for facilitating the reset operation by using an oxygen-rich composition on the anode side of the resistance change film to advance anodic oxidation is proposed in Z. Wei, Y. Kanzawa, K. Arita, K. Katoh, K. Kawai, S. Muraoka, S. Mitani, S. Fujii, K. Katayama, M. Iijima, T. Mikawa, T. Ninomiya, R. Miyanaga, Y. Kawashima, K. Tsuji, A. Himeno, T. Okada, R. Azuma, K. Shimakawa, H. Sugaya, T. Takagi, R. Yasuhara, K. Horiba, H. Kumigashira, and M. Oshima, IEDM2008, pp. 293-296. However, even in this method, the reset current is not sufficiently reduced. In particular, with the downscaling of the device, the effect of reset current reduction is decreased, leaving room for improvement.